Inductance coil and method of manufacture thereof



March 19, 1935. F. E.'ROBINYSON Filed April 19, 1935 Fig 2 12y 5 (POLUdEIEd [rm latex Ca e.

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RN EY Patented Mar. 19, 1935 PATENT OFFICE INDUCTANOE COIL AND METHOD OF MANUFACTURE THEREOF Francis Edward Robinson, Colchester, England, assignor to Radio Corporation of America, a corporation of Delaware Application April 19, 1933, Serial No. 666,867 In Great Britain April 23, 1932 8 Claims.

This invention relates to inductance coils and methods of manufacture-thereof. More specifically the invention relates to coils of the type sometimes termed field-less coils, i. e. toroidal coils or coils having complete low reluctance magnetic circuits and so formed or constructed that there is no. magnetic field or at any rate relatively little magnetic field exterior of the coil. Field-less coils are commonly employed in wireless telegraph apparatus and in telephone equipment and for similar purposes, one of the principal objects of the provision of such coils being to provide inductances without any substantial coupling to other nearby inductive apparatus. Although such coils are, as above stated, commonly described as field-less coils, in practice there is almost always an external field of some magnitude.

The present invention has for its object to provide a simple cheap and easily manufactured socalled field-less coil structure whose external field shall be very small indeed and substantially zero.

According to this invention a process for the manufacture of a so-called field-less coil includes the steps of winding a coil and filling the wound coil with a mixture of a binding material and dust of magnetic material, and then solidifying the binding material. Preferably the binding material is latex and the solidification thereof is accomplished by vulcanizing.

A preferred manner of filling the wound coil is to immerse it in a mixture of latex or other binding material and magnetic dust so that the dust is permitted to settle in and round the coil, current being fed through the coil during the settling process so that the particles of magnetic material take up their correct magnetic positions.

In the drawing, Figure 1 shows diagrammatically a step of applicants invention wherein the coil is shown wound on a former;

Figure 2 shows the former removed and the coil shaped as desired; and,

Figure 3 illustrates in diagrammatic form an end view of the completed inductance coil.

In one way of carrying out the present invention illustrated in Figures 1 to 3 a coil 1 is wound on a straight former 2 (Figure 1) in a plurality of layers. As each layer is wound on, latex is brushed over, and when the winding is complete the coil is dipped in latex and then placed in an oven and wholly or partly vulcanized. The coil is now removed from the oven and the former withdrawn from the coil after which the said coil is again dipped in latex to obtain a coating inside the said coil and then bent around into toroidal shape or approximately toroidal shape as shown in Figure 2, the coil, however, not being bent into the full circle, i. e. being left with the ends not touching one another. The bent approximately toroidal coil is now placed in a deep glass container and a mixture of latex and iron dust poured into the container. The iron dust will gradually fall to the bottom of the container and fill up the coil. During this settling process current is passed through the coil so that the particles of iron take up their current magnetic positions. The iron is allowed to settle until the coil is completely covered after which the surplus latex is poured chi and the container with the coil therewithin placed in an oven to accelerate vulcanization. The final appearance of the finished vulcanized coil structure is that of a solid disc (see Figure 3 which is an edge view of the disc it being understood that the disc may be solid or angular as desired) and it will be seen that in view of the position of the iron relative to the winding there will be substantially no external field when the coil is in use.

For a coil for use at audio frequencies the following proportions of iron dust to latex were successfully employed: 80 parts (by weight) iron dust, 20 parts (by weight) latex. In this particular example it was sought to obtain as large a proportion of iron dust as was (in the particular case in question) consistent with the obtaining of a required low value of resistance at the higher audio frequencies and, of course, the invention is not limited to the particular proportions given since the choice of proportions will be dictated by design requirements.

It is believed that owing to the fact that latex is in the form of small spheres of material of about 1/ 10.000 of an inch in diameter (which float in water) these small spheres fill up the large number of tiny spaces in the iron dust and thus bind the iron dust together in much the same way as that in which cement fills up the tiny spaces in sand when making concrete.

The invention is not limited to the use of latex and rubber compounds other than latex have been successfully employed more particularly for mixing with the iron dust. It is believed however that latex is the most convenient material for building up the coil itself as distinct from mixing with the iron dust. Latex is of course also suitable for mixing with the iron dust.

In a further manner of carrying out the invention a paste of iron dust and latex or like binding material is made and the coil is filled 2. with this paste before being bent round into approximately toroidal shape.

In an alternative method of construction a toroidal coil is not employed, an ordinary flat wave wound winding coil being utilized. Iron dust and latex or the like are allowed to settle round this wave wound coil as in the above described process and the latex carrying the iron dust is vulcanized also as above described.

I claim:

1. A process for the manufacture of a so-called fieldless cofl, said process including the steps of winding a coil filling in the wound coil with a mixture of a binding material and dust of magnetic material, and tlien solidifying the binding material.

2. A process as claimed in claim 1 and in which the binding material includes latex and the solidification thereof is accomplished by vulcanizing.

3. A process as claimed in claim 1 and in which the coil is filled in by immersing it in a mixture of a binding material and magnetic dust, allowing the dust in the mixture to settle in and round the coil, and passing an electric current through the coil during the settling process so that the particles of magnetic material orient themselves magnetically.

4. A process for the manufacture of a so-called fieldless coil said process comprising the steps of winding a coil in a plurality of layers upon a straight former, brushing a binding material on the coil as each layer is wound thereon, dipping the coil in a binding material when the winding is complete and partially solidifying the binder,

withdrawing the former and re-dipping the coil in a binding material, bending the re-dipped coil into substantially toroidal shape but with its ends not touching one another, immersing the bent coil in a binding material and pouring in iron dust and passing current through the coil while the particles of iron are settling, removing surplus binding material (ii' any) and solidifying the resultant filled in coil.

5. A process for the manufacture of inductance coils, loading coils and the like which includes the steps of winding a coil, immersing the wound coil in a mixture of binding material and finely divided magnetic material so that the coil is, so to speak, filled with the mixture, and solidifying the binding material while under the influence of a magnetic field.

6. A process as claimed in the next preceding claim in which the magnetic field is produced by passing current through the wound coil.

'7. A process for the manufacture of so-called fieldless coils, said process including the steps of winding a coil, filling in the wound coil with a mixture of a binding material and finely divided magnetic material, magnetically orientating the particles of magnetic material in the mixture by a magnetic field and solidifying the binding material.

8. A process as claimed in the next preceding claim and in which the magnetic field is produced by passing a current through the winding itself.

FRANCIS EDWARD ROBINSON. 

